An optical receiver for use in an optical communication system includes, for example, a photodetector, a transimpedance amplifier (TIA), and a feedback amplifier (amplifier). As the photodetector, a photodiode is used. The photodetector converts an optical signal into an electrical signal (photocurrent). The TIA converts the photocurrent (a current signal) output from the photodetector into a voltage signal. The feedback amplifier automatically controls an offset of the TIA (automatic offset control). U.S. Pat. No. 7,230,476 discloses a feedback amplifier including a diode, a differential amplifier (operational amplifier), and a capacitor. The diode is reverse-biased and connected between an input terminal of the feedback amplifier and the operational amplifier. The capacitor is connected between an input and an output of the operational amplifier to configure a feedback loop. Large resistance of the reverse-biased diode and large capacitance of the feedbacked capacitor provides a low pass filter with a low cutoff frequency. The low pass filter stabilizes automatic control of an offset of the feedback amplifier. Further increasing of an input impedance of the feedback amplifier to lower the cutoff frequency reduces an input current of the operational amplifier. The differential amplifier with a Darlington connection has the advantage of amplifying such a small input current, but requires a relatively large supply voltage that prevents the differential amplifier from reducing power dissipation thereof.